Buggy code:
@ SuppressWarnings ( "restriction" ) public class MobileSearchPanelPresentation extends AbstractLayoutPresenter < ComponentContainer > implements IFilterProvidingPresentation { private static final Logger LOGGER = LoggerFactory . getLogger ( MobileSearchPanelPresentation . class ) ; private HorizontalLayout horizontalLayout ; private FormLayout leftForm ; private FormLayout rightForm ; private MobileSearchPanelPresentation . ModelAccess modelAccess ; private int currentChildIndex ; public MobileSearchPanelPresentation ( IElementEditpart editpart ) { } @ Override protected void doUpdateLocale ( Locale locale ) { } protected void applyCaptions ( ) { } protected void refreshUI ( ) { } private void addChild ( IEmbeddableEditpart child ) { } @ Override public ComponentContainer doCreateWidget ( Object parent ) { if ( ( horizontalLayout ) == null ) { horizontalLayout = new HorizontalLayout ( ) ; setupComponent ( horizontalLayout , getCastedModel ( ) ) ; associateWidget ( horizontalLayout , modelAccess . yLayout ) ; if ( modelAccess . isCssIdValid ( ) ) { horizontalLayout . setId ( modelAccess . getCssID ( ) ) ; } else { horizontalLayout . setId ( getEditpart ( ) . getId ( ) ) ; } if ( modelAccess . isMargin ( ) ) { horizontalLayout . addStyleName ( CSS_CLASS_MARGIN ) ; horizontalLayout . setMargin ( true ) ; } if ( ! ( modelAccess . isSpacing ( ) ) ) { horizontalLayout . setSpacing ( false ) ; } else { <START_BUG> horizontalLayout . setData ( CSS_CLASS_SPACING ) ; <END_BUG> horizontalLayout . setSpacing ( true ) ; } if ( modelAccess . isCssClassValid ( ) ) { horizontalLayout . addStyleName ( modelAccess . getCssClass ( ) ) ; } else { horizontalLayout . addStyleName ( CSS_CLASS_CONTROL ) ; } horizontalLayout . addStyleName ( CSS_CLASS_HORIZONTALLAYOUT ) ; leftForm = new FormLayout ( ) ; leftForm . setSizeFull ( ) ; horizontalLayout . addComponent ( leftForm ) ; rightForm = new FormLayout ( ) ; rightForm . setSizeFull ( ) ; horizontalLayout . addComponent ( rightForm ) ; createBindings ( modelAccess . yLayout , horizontalLayout , null ) ; initializeChildren ( ) ; renderChildren ( false ) ; } return horizontalLayout ; } @ Override public Object getFilter ( ) { } private void initializeChildren ( ) { } @ Override public ComponentContainer getWidget ( ) { } @ Override public boolean isRendered ( ) { } @ Override protected void internalDispose ( ) { } @ Override public void doUnrender ( ) { } @ Override protected void internalAdd ( IEmbeddableEditpart editpart ) { } @ Override protected void internalRemove ( IEmbeddableEditpart child ) { } @ Override protected void internalInsert ( IEmbeddableEditpart editpart , int index ) { } @ Override protected void internalMove ( IEmbeddableEditpart editpart , int oldIndex , int newIndex ) { } @ Override public void renderChildren ( boolean force ) { } protected void unrenderChildren ( ) { } private static class ModelAccess { private final VMSearchPanel yLayout ; public ModelAccess ( VMSearchPanel yLayout ) { } public String getCssClass ( ) { } public boolean isCssClassValid ( ) { } public boolean isSpacing ( ) { } public String getCssID ( ) { } public boolean isCssIdValid ( ) { } public boolean isMargin ( ) { } } }

Fix:
horizontalLayout . addStyleName ( CSS_CLASS_SPACING ) ;